1. Field of the Invention
The invention relates in general to an overdrive data modifier and method of looking up thereof, and more particularly to an overdrive gray level data modifier and method of looking up thereof.
2. Description of the Related Art
With the features of thinness, lightweight, compactness, and low radiation, liquid crystal display (LCD) has been widely used in recent years. Refer to both FIG. 1A and FIG. 1B. FIG. 1A is a timing diagram of gray values of liquid crystal molecules, and FIG. 1B is a timing diagram of input voltages. When the liquid crystal molecules are driven by an input voltage V1, the gray value of liquid crystal molecules is L1, and when the liquid crystal molecules are driven by an input voltage V2, the gray value of liquid crystal molecules is L2.
When the input voltage is converted from voltage V1 to V2 at time point t1, the gray value of liquid crystal molecules is converted to L2 from L1. Due to the characteristics of the liquid crystal molecules, the required time for the gray value to be converted from L1 to L2 is from time point t1 to time point t3, and the behavior of the gray values is illustrated in the curve C1. When time point changes from t4 to t6, the voltage value V2 is converted to V1, enabling the gray value of liquid crystal molecules to be converted from L2 to L1 as illustrated in the curve C3. However, facing the increase in resolution and display frequency, the change rate in the gray value of liquid crystal molecules would be too slow thus resulting in a residual image, if the change rate of the gray value of liquid crystal molecules still behavior as in the curve C1. Therefore, an overdrive method is provided. At time point t1, the original input voltage V2 used to drive the liquid crystal molecules is displaced by an overdrive input voltage V2′ so that the required time for the gray value to be converted from L1 to L2 is reduced to be as short as from time point t1 to time point t2, and then the input voltage V2 is resumed again as shown in the curve C2. Similarly, at time point t4, the original input voltage V1 used to drive the liquid crystal molecules is displaced by an overdrive input voltage V1′ so that the required time for the gray value to be converted from L2 to L1 is reduced to be as short as from time point t4 to time point t5, and then the input voltage V1 is resumed again as shown in the curve C4.
When simply providing the liquid crystal molecules with overdrive input voltage V1′ and V2′, the corresponding overdrive gray values OD are recorded, and the overdrive gray values OD along with the correspondence relationship between the previous gray level compared value PF and the current gray level compared value CF are recorded together to form an overdrive look-up table. The overdrive gray value OD used when converting a gray value can be determined according to the overdrive look-up table. In terms of the gray value 256, the overdrive look-up table formed by the previous gray level compared value PF and the current gray level compared value CF contains 256*256 items of overdrive gray values OD. The data volume being too large is reduced to a 17*17 overdrive look-up table, so that an overdrive data modifier capable of reducing the overdrive look-up table can be achieved. Referring to FIG. 2, a 17*17 overdrive look-up table is shown.
However, if the previous frame gray level data equals to 180, and the current frame gray level data equals to 70, it can be looked up from the FIG. 2 that the corresponding overdrive gray value OD when the current gray level compared value CF equals to 64 and the previous gray level compared value PF equals to 176 is 24, that the corresponding overdrive gray value OD when the current gray level compared value CF equals to 64 and the previous gray level compared value PF equals to 192 is 16, that the corresponding overdrive gray value OD when the current gray level compared value CF equals to 80 and the previous gray level compared value PF equals to 176 is 48, and that the corresponding overdrive gray value OD when the current gray level compared value CF equals to 80 and the previous gray level compared value PF equals to 192 is 40. According to the four overdrive gray values OD, namely 24, 16, 48 and 40, the required overdrive gray level data are obtained by using interpolation to overdrive the liquid crystal molecules. The corresponding overdrive gray value OD obtained, using the interpolation according to the two overdrive gray values 24 and 16, is 22. The formula is expressed as:24−[(24−16)/16]*(180−176)=22;
The corresponding overdrive gray value OD obtained, using the interpolation according to the two overdrive gray values 48 and 40, is 46. The formula is expressed as:48−[(48−40)/16]*(180−176)=46; and
The last overdrive gray value OD obtained, using the interpolation according to the two overdrive gray values 22 and 46, is 31. The formula is expressed as:22+[(46−22)/16]*70−64)=31.
The memory unit used in an overdrive data modifier is normally a static random access memory (SRAM) or a read only memory (ROM). Since four overdrive gray values OD require four times of reading, the reading rate of the memory unit is usually too slow to achieve the object of accessing the overdrive gray values OD within one clock cycle.